-

Nasarsquos

ChaNdra X ray ObservatOry

the sOlar system ThrOugh ChANDrArsquoS EyES

Earth

IllustratIon

One star eight planets and

a myriad of moons comets

and asteroids This is the

Earthrsquos local neighborhood

known as the Solar System

Despite studying this system

for centuries astronomers

still yearn to know much

more NASArsquos Chandra

X-ray Observatory is

providing new insight and

uncovering new mysteries

about objects of all sizes

and across all distances

throughout our Solar System

the sOlar system thrOugh ChaNdrarsquos eyes

Chandrarsquos specialty is probing

the super-hot regions around

exploding stars galaxies or

black holes But Chandra has

also shown that the relatively

peaceful realms of space such

as our Solar System sometimes

shine in X-ray light

Planets satellites and comets

typically have temperatures

well below 1000 degrees but

they still can produce X-rays

in a number of ways most of

which involve the Sun directly

or indirectly Although the X-ray

power is relatively weak it

provides information difficult to

come by with other telescopes

Nasarsquos ChaNdra X -ray ObservatOry

Learn more at httpchandraharvardedu

NASArsquos Marshall Space Flight Center huntsville

Ala manages the Chandra program for the

agency rsquos Science Mission Directorate The

Smithsonian Astrophysical Observatory controls

science and flight operations from the Chandra

X-ray Center in Cambridge Mass

Chandra X-ray Images Earth NASAMSFCCXCABhardwaj et al Earth model NASAgSFCLPerkins amp gShirah Titan NASACXCPenn StateKMori et al The Moon NASACXCSAOJDrake et al Venus NASAMPEKDennerl et al Comet C1999 S4 (LINEAr) NASACXCCLisse SWolk et al Jupiter NASACXCSWrIgrgladstone et al Mars NASACXCMPEKDennerl et al Saturn NASAuhamburgJNess et al OptICal Images Titan NASAJPLSpace Science Institute The Moon robert gendler Venus Konrad Dennerl Comet C1999 S4 NASA hWeaver and PFeldman (Johns hopkins univ) MArsquohearn (univ of Maryland) CArpigny (Liege univ) MCombi (univ of Michigan) MFestou (Obs Midi-Pyrenees) and g-P Tozzi (Arcetri Obs) Mars NASA JBell (Cornell) MWolff (SSI) and The hubble heritage Team (STScIAurA) Jupiter NASAhSTrBeebe et al Saturn NASASTScI The Sun NASASOhO IllustratIOns Inside NASASOhO Back CXCM Weiss

-

-

-

mdash

-

-

-

--

-

-

earth Very close to home Chandra has detected X-rays from auroras in the Earthrsquos north polar regions The auroras are generated by solar storms that disturb the Earthrsquos magnetic field and energize electrons high in the Earthrsquos atmosphere As some

of these electrons spiral along Earthrsquos magnetic field lines they collide with atoms above the north polar regions and produce X-rays Chandra has also detected evidence of X -rays from Earthrsquos geocorona (extended outer atmosphere) through which Chandra moves The geocor -

onal X-rays are caused by collisions between hydrogen atoms in the geocorona with carbon oxygen and neon ions that are streaming away from the Sun in the solar wind This process is called ldquocharge exchangerdquo because an elec -tron is exchanged between a neutral atom in the atmosphere and an ion mdashtypically carbon nitrogen or oxygen mdashin the solar wind After such collisions X-rays are emitted as the captured elec -trons move into tighter orbits These X-rays have an energy that is equal to the difference in energy states for the electron orbits The spectrum or overall distribution of X -rays with energy from charge exchange collisions can be distinguished from other pro -cesses with a sensitive X-ray spectrometer and provide evidence that the charge exchange collision is occurring

the sOlar system thrOugh ChaNdrarsquos eyes

Illustration of solar Wind the white lines represent the

solar wind the purple line is the bow shock produced by

the interaction of the solar wind with the earthrsquos protective

magnetosphere (blue lines) [not to scale]

COmets The charge exchange process operates throughout the Solar System It is especially important for comets which have extended atmo spheres Comets resemble ldquodirty snow ballsrdquo a few miles in diameter with a surrounding cloud of dust and gas By observing X rays due to charge exchange in the cometary atmosphere it is possible to study the elements

present in the solar wind the structure of the cometrsquos atmosphere and cometary rotation In the future it may be possible to detect X radiation from collections of hundreds of comets around stars other than the Sun young stars would be the most promising candidates because they have vigorous stellar winds

the mOON Chandra has been used to prospect for elements on the Moon X-rays from the Moon are caused by ldquofluorescencerdquo due to the im -pact of solar X-rays on the surface of the Moon When a solar X-ray is ab -sorbed by an atom on the lunar surface the X -ray knocks an electron out of the inner part of the atom and excites the atom to a higher energy level The atom almost immediately returns to its lower energy state with the emission of a fluorescent X -ray In a similar way ultraviolet light produces the visible light of fluorescent lamps The energy of a fluorescent X-ray is unique to

the particular type of atom so fluorescent X-rays give a direct measurement of elements present independent of assumptions about the type of mineral or other complications Oxygen magnesium aluminum and silicon were detected over a large area of the lunar surface Longer observations of the Moon with Chandra should help to determine if the Moon was formed by a giant impact of a planetoid with the Earth about 45 billion years ago or by some other process

veNus The X-rays from Venus and to some extent the Earth are due to the fluorescence of solar X -rays striking the atmosphere Chandrarsquos image of Venus shows a half crescent due to the relative orientation of the Sun Earth and Venus Solar X-rays are absorbed about 120 kilometers above the surface of the planet knocking electrons out of the inner parts of atoms

and exciting the atoms to a higher energy level When the atoms almost immediately return to their lower energy state they emit a fluorescent X -ray In contrast to the X -radiation the optical light from Venus is caused by the reflection of sunlight from clouds 50 to 70 kilometers above the surface

mars Fluorescent X-rays from oxygen atoms in the Martian atmo -sphere probe heights similar to those on Venus A huge Martian dust storm was in progress when the Chandra observations were made Since the intensity of the X -rays did not change when the dust storm rotated out of view astronomers were able to conclude that the dust storm did not affect Marsrsquos upper atmosphere They also found evi -

dence that Mars is still losing its atmosphere into deep space A faint halo of X-rays was also detected some 7000 kilo -meters above the surface of Mars These X -rays are presumably due to the solar wind charge exchange process operating in the tenuous extreme upper atmosphere of Mars

Jupiter Jupiter has an environment capable of producing X-rays in a different manner because of its substantial magnetic field X -rays are produced when high-energy particles from the Sun get trapped in its magnetic field and accelerated toward the polar regions where

they collide with atoms in Jupiterrsquos atmosphere Chandrarsquos image of Jupiter shows strong concentrations of X -rays near the north and south magnetic poles The weak equatorial X -ray emission is likely due to reflection of solar X-rays

saturN Like Jupiter Saturn has a strong magnetic field so it was expected that Saturn would also show a concentration of X-rays to ward the poles however Chandrarsquos observation revealed instead an increased X-ray brightness in the equatorial region Furthermore Sat urnrsquos X-ray spectrum or the distribution of its X-rays according to ener gy was found to be similar to that of X-rays from the Sun This indicates

that Saturnrsquos X-radiation is due to the reflection of solar X-rays by Saturnrsquos atmosphere the same process that may be responsible for the weak equatorial X-radiation observed from Jupiter Fur ther observations should help clarify whether Saturnrsquos magnetic polar regions ever flare up in X-rays as do Jupiterrsquos

titaN Astronomers have used the lack of X-rays from Saturnrsquos larg -est moon Titan to draw some interesting conclusions On January 5 2003 Titanmdashthe only moon in the Solar System with a thick atmo -sphere mdashcrossed in front of the Crab Nebula a bright extended X -ray source Titanrsquos transit enabled Chandra to image the one-arcsecond-diameter X-ray shadow cast on Chandra by the moon This tiny shadow corresponds to the size of a dime as viewed from two and a half miles The diameter of Titanrsquos shadow was found to be larger than the known

diameter of its solid surface This difference in diameters yields a measurement of about 880 kilometers for the height of the X-ray absorbing region of Titanrsquos atmosphere The extent of Titanrsquos upper atmosphere is consistent with or slightly (10-15) larger than that implied by Voyager I observations made at radio infra -red and ultraviolet wavelengths in 1980 Saturn was about 5 closer to the Sun in 2003 so increased solar heating of Titan may have caused its atmosphere to expand

the suN The Sunrsquos corona or hot outer atmosphere produces X-rays but it is too close and bright for Chandra to observe with its extremely sensitive detectors An X-ray image of the Sun courtesy of The Soft X-ray Telescope on board the

yohkoh satellite is shown on the right This telescope was specially designed to study the solar corona which has a temperature of about 2-million-degrees Celsius

From small rocky comets to large gas

eous planets the Solar System is alive in

X ray light When combined with optical

images (below) Chandrarsquos X-ray data ex

pand the understanding and pose new

questionsmdashabout the Solar System

[Images not to scale]

tItanrsquos path

tItanrsquos shadOW

httpChaNdraharvardedu

the sOlar system